Child Protective Services investigated more than three million cases of suspected child abuse in 2007, but a new study suggests that the investigations did little or nothing to improve the lives of those children.

In 1973, Congress passed the Child Protective Services Act, designed to encourage more thorough and accurate reporting and record-keeping in child abuse cases. In New York, for example, there are now Child Protective Services offices in every county, paid for in part with federal funds.

Researchers examined the records of 595 children nationwide, all at similar high risk for maltreatment, tracking them from ages 4 to 8, 164 that were investigated for suspected abuse or neglect, and 431 families that had not been investigated. The scientists then interviewed all the families four years later.

The scientists looked at several factors: social support, family functioning, poverty, caregiver education and depressive symptoms, and child anxiety, depression and aggressive behavior — all known to increase the risk for abuse or neglect. They were unable to find any differences in the investigated families compared with the uninvestigated in any of these dimensions, except that maternal depressive symptoms were worse in households that had been visited.

One possible interpretation of this result would be that the investigated families were at greater risk to begin with, and that the investigation helped them to recover to the expected level of risk. But if this were so, the authors write, households with recent investigations would have greater risk than households with more distant investigations. Statistical analysis found no such association. They concluded that Child Protective Services investigations had little or no effect.

The researchers were in some ways unsurprised by their findings. Even when services are offered, they usually take aim at immediate risks — substance abuse, or domestic violence — not abiding problems like poverty or poor social support. Whatever interventions were offered apparently failed to reduce the risk for future child abuse.

Dr. Kristine A. Campbell, the lead author of the study, said that it may be too easy to blame Child Protective Services. “I believe that C.P.S. has a critical role,” she said. “As a pediatrician, when I’m there in the middle of the night with a child who has been beaten up, I need them. But we have to look at other systems that can really create a safety net for these children.”

Still, C.P.S. serves an important role in gathering information. This study supports the idea that it is time for further discussion of the role of protective services, beyond investigation.The difficulty is, that C.P.S. is charged with dealing with acute issues. We do not have a means for C.P.S. to deal with the chronic, underlying issues.

The study appears in the October issue of The Archives of Pediatrics & Adolescent Medicine, has certain weaknesses: some potentially modifiable risk factors — intimate partner violence and substance abuse, for example — were not included in the data they used. And not all of the five different geographical sites systematically collected information on all risk factors.

Dr. Abraham B. Bergman wrote an editorial that was published with the study: “Child Protective Services Has Outlived Its Usefulness,” and suggests some essential changes:

child abuse is a crime and should be investigated by the police

public health nursing services should be the first to respond to concerns of child neglect

social workers should assess appropriate living situations and work with families to obtain services